Radar target simulator



F. B. UPHOFF 2,934,759

RADAR TARGET SIMULATOR 3 Sheets-Sheet 2 ODI. OnTl wwo April 26, 1960 Filed May 1 April 26, 1960 Filed 'nay 1. 195s,

couPAnATon ems LEYEL esssarmm sELEcTED ouTPuT AzmuTnAL I ANTENNA OOMPARATOR OUTPUT -18 IST OIFFERENTIATING AMPLIFIER OUTPUT -19 3 Sheets-Sheet 3 CLIPPER OUTPUT 21 MONO-STABLE MULTIIVIBRATOR PULSE OUTPUT 26 GATE AMPLIFIER OUTPUT21 BLOOKINO OSCILLATOR OUTPUT -29 Fig. 3

INVENTOR.

FRANK B. UPHOFF ATTORNE YS RADAR TARGET-SIMULATOR Frank n. Uphorr, churchviue, Pa., assignor to are United States of-America as represented by the Secretary of Ithe Navy Application May 1, 1958, Serial No. 7 32,405 10 Claims. (Cl. 343-173) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without any payment of royalties thereon or therefor.

- .The present invention relates to a radar target'sirnulator and more particularly to a radar target simulator vfor generating an artificial target which closely resembles the essential characteristics of areal target.

In order to ymaintain optimum performance' of f an loverall radar system', various ancillary devices areemployed to ascertain the functional merits of associated component equipment. ing power and sensitivity measurements are an invaluable adjunct; As an'aid to the training of radar operators or to determine their alertness, various types of radar target simulators have been designed. A known type employs a perforated sheet of otherwise opaque material which is interposed between a light source and a photoelectric f .y cell.. Video signals correspondingl .to 'they perforations tive instrumentality provides for the generation,l of a pulse modulated RF signal which closely simulates the essential cli'ar'acteristics of a real target signal.r Provision is? made forconformingthe character of the RF signalv with radar antenna pattern jbeamwidth. Appropriate V'structure 4responsive to antenna position is also'providedfforv injection vof the simulated rtarget signal intothe RF section of the radarv system at arbitrary azimuth'.y Inadditi'on,

vthe instant invention embodies trigger* delay means in Y order to simulate target range.y Thus, as herein summarily set forth, ,the inventive radar-target simulator-not only provides for tunableelements ofthe radar systemto 'be peaked for best operation, but also, operator alertness may be monitored at any` time. Hence,r inthis manner, the maintenance of optimum overall operational efiiciency of aV radar system more readily achieved.

x -An object of the present invention is'theVV provision of Y a radar target simulator for generating, anfartifi'cial target l whichclosely simulates the essential characteristics `of the real target.

United' States 'Patent In this respect, test setsfor mak- Another object is toprovide'raradartargetsimulator 1 for generating an artificial'y target havingsp'ecific characteristics' which conform'with radar antennapattern beam- Width.. Y

1 Alfrther object offtl'ie invention is `the:provi"sionfofja radar target simulator for'generati'ng'an artificial target ,ICC

which may be injected into the radar system for presentation on a PPI screen at arbitrary azimuth and range.

Still another object is to provide a radar target simulator for generating a pulse modulated RF signal inwhich characteristics corresponding to radary antenna ifpattern beamwidth may be selectively controlled.

A final object of the present invention is the provision of a radar target simulator for generating a pulse modulated RF signal which may be injected into the RF section of the radar system as a test signal for simultaneous viewing on a PPI screen at arbitrary azimuth and range withV i radar video signals. v Y

The exact nature of this invention as Wellvas other objects and advantages thereof will be readily apparent4 from consideration of the following specication relating to the annexed drawing in which:

,Fig 1 is a functional block diagram offa preferred Y embodiment of the radar target simulator, illustrating in particular the cooperative relation of the. inventive apparatus with. specific elements of a radar system.V

IFig. 2 is an electrical schematic diagram of 'the principally novel structure of the inventive radar target simulator, and

Fig. 3 depicts Aa timing chart showing in relative amplitude and timing relation the various waveformsk which are developed in the radar target simulator. f

Referring now to the drawings, whereinlike reference characters designate like or corresponding parts throughout the several views, there is shown in Fig. 1 a potentiometer R11 of a type designed for continuous rotation. The wiper of this potentiometer is illustratedft'o derive its rotation from the radar antenna assembly 12 as 'rep-i resented by the dotted linenotation. The antenna aslsembly 12 of a search radar system is? schematically 'Y illustrated in Fig. l to comprise a stationary R13-transmission line 13A which is coupled to rotary Afeeder 14A byy means of aV rotating joint, not herein illustrated. vNumeral 15 designates conventional drivingmeansfor" ldriyi'ng the antenna. A directional coupler 16 islem'ployed for injecting the RF signal generated by the inventive apparatus. It should be understoodY that-rotation yof the wiper of potentiometer Rlmayybe'obtained elsewhere. For'- example in radar systemsV whereinV arot'ating deflection yokeI is employed, the potentiometerwiper mayV be suitably mechanically connected to the mechanism'gwhichV drives the yoke.

Withrespectto Fig. 1,- it is evident thata voltage r'epresentative of azimuthal antenna position-"will'be-developed. Cathode follower 17 acceptsithis voltageand supplies it at low impedance to amplitude comparator 18.Y 'I'his latter stage producesa signal-which is displaced in time position coterminously withjselected az'imuthal antennaposition. This ysignal is subjected towaveshaping by a rst differentiating ampliiier19, diode clipper 21, and a second diferentiating amplifier 22.* Successivev .i

amplification is performed by amplifier stages 23 and 524',

rendering the signal Lof proper amplitude and phase' for firing blocking oscillator 25. A spik'elike voltage excursion is produced whichcauses monostable multivibrator 26 to develop a-substantially' squar'ewave pulse having-.ia Y

'time duration conforming with antenna pattern-beamwidth. vThis squarewave voltager serves, as a conditioning level for gateamplifier 27, which is coupled tofa source of periodically recurring radar triggers, available;

in the radar set, for example, at the pulsesynchronizer. y unit thereof. AmplifierV k,27' thereby becomes re'c`i`e`pftive,'V allowing a discrete numberrof radar triggers to, beine-- cepted. These. triggers'gare inverted andV amplified rby amplifier 28,' which linitiates operation o f 'blocking oscilllator 29. A corresponding burstof spikelike vo'ltageexcursions is produced.4 '(athldeifollower Sl'bes'idefservg Patented Apr.y26,' v1960 K ing an isolation function supplies these excursions at low impedance to microwave generator 32, which incorporates an amplitude control 30 and a delay control 33. The pulse modulated RF signal developed by generator 32 is fed to directional coupler 16.

Referring next to Fig. 2 wherein the pertinent structural details of the inventive apparatus are more particularly set forth, the grid element of section V1A of cathode follower 17 is connected to the wiper of potentiometer R11. With respect to the nomeclature herein utilized, V1A and V1B represent corresponding sections of a vacuum tube having a double set of elements. A low impedance replica of the voltage across R11 is developed across R38. Amplitude comparator 18 ernploying a diode V2A effects comparison of the voltage across R38 with a predetermined bias level established by the position of the wiper of potentiometer R34. The bias available across R34 falls within a potential range which corresponds with to 360 of antenna rotation. Potentiometers R35 and R36 which are connected in series therewith precisely establish the limits of this potential range, with R37 comprising the principal load for stage 18. Successive differentiation of the output voltage of comparator 18 is performed by differentiating feedback amplifier stages 19 and 22 rather than by passive resistive-capacitive elements. Because of the relatively long pulse periods involved, the use of passive elements for differentiation fails to produce an acceptable output. A proportionate amount of voltage feedback is coupled through R44 and R53 to the respective inputs of these pentode stages. Potentiometer R41 furnishing screen voltage for the first differentiating amplifier 19 is adjusted to render the junction of R45 and R46 at approximately zero potential. The diode clipper 21 is employed to furnish a low impedance path, shunting to ground any positive signal appearing at the anode of VZB. The output of the second differentiating amplifier 22 appears at the junction of R55 and R56, being fractionated according to the ratio of the value of these resistances. Amplifiers 23 and 24 are entirely conventional, each utilizing a D.C. restorer at the respective inputs thereof. Diode V7A with coupling capacitor C54 and resistor R57 provide for positive clamping of the signal at the grid input of VSA, while in comparable manner, diode V7B with C61 and R62 provide negative clamping for amplifier 24. C63 improves the waveform appearing across grid load resistor R62. Blocking oscillator 25 is normally quiescent by virtue ofa cutoff bias supplied from a biasing voltage divider, R68 and R69, through R71. The blocking oscillator is triggered into operation by the aforesaid waveform which is coupled through the impedance comprising R65 and C66. R65 functions as an isolation resistor, which minimizes interaction between amplifier 24 and blocking oscillator 25. A transformer T73 having a tertiary winding is used, a sharp spikelike voltage being developed in the output winding thereof. Monostable multivibrator 26 is capacitively coupled by C74 to the output winding of transformer T73 and produces a positive substantially squarewave output voltage having a duration determined by the RC time constant of C82, R83, and the bias potentiometer R77, the latter serving as an antenna pattern beamwidth control. A D.C. restorer VA is employed to remove effects of averaging by C74. The gate amplifier 27 which follows is rendered conductive only during the interval when multivibrator 26 produces a positive monostable pulse. The suppressor grid of V11 is tied to a negative point on a divider consisting of R88 and R89. Positive clamping of the signal is provided at a level determined by the potential at the junction of these resistors. The potentiometer R91 precisely controlsY conduction through pentode V11. Positive radar triggers occurring at the pulse repetition frequency (PRF) are impressed on the grid input through C95. The plate resistor R92 is the load for this stage across which amplified radar triggers of negative polarity are developed. Amplifier 28 comprising a conventional triode stage functions essentially as a phase inverter which is instrumental in triggering blocking oscillator 29 into operation. The blocking oscillator 29 is normally quiescent until pulsed and employs a tertiary wound transformer T111 as in the previous instance. A cathode follower 31 accepts the positive spikelike voltage from the output winding of T111 and develops a low impedance replica of this signal across cathode resistor R112.

The signal developed across R112 is supplied as a modulating pulse to microwave generator 32, illustrated in Fig. l. Generator 32 in Fig. l may be of conventional design employing a tunable-klystron or other type of oscillator means. Numeral 30 represents an output control effective to control the amplitude of the RF output signal. The RF attenuation means incorporated in generator 32 may comprise simply a fiap type attenuator, or may be a movable coupling loop which supplies an RF signal proportional with the degree of coupling with the field in the klystron. Control 33 represents a pulse delay control utilizedto effect a predetermined amount of delay relative to the radar triggers, thereby providing for target range in the simulated target signal. This -delay may be conventionally obtained by means of a Miller integrating circuit, phantastron, or other type of ,linear delay circuit such as the monostable multivibrator 26 of the instant invention. The modulated RF output of microwave generator 32 is fed to directional coupler 16 wherein unilateral injection of the signal takes place.

Operation of the inventive radar target simulator is best set forth in connection with waveforms a through j depicted in relative amplitude and time relation in Fig. 3. With reference to Fig. l, a sawtooth voltage waveform a in Fig. 3 is developed linearly with rotation of the antenna assembly 12 at the wiper of potentiometer R1-1. This sawtooth voltage is supplied to cathode follower 17. A low impedance replica of this voltage appears across R38 in Fig. 2 and is applied to the anode of V2A of amplitude comparator 18. Depending on the setting of bias potentiometer R34, V2A remains in' a non-conductive state until the sawtooth voltage exceeds the comparator bias level, indicated in Fig. 3. When the anode of V2A is positive relative to its cathode, the diode conducts and a comparator output voltage, waveform b, is developed across R37. Hence, the sawtooth waveform b is initiated as a function of the bias setting of R34 and antenna position. Thus, R34 performs the function of azimuth control effective to insert the simulated target signal at any desired azimuth.

The first differentiating amplifier 19 operates on the sawtooth waveform b and produces a voltage which is substantially squarewave in character, as indicated by waveform c in Fig. 3. Waveform d is representative of the negative pulse voltage appearing at the anode of diode clipper 21, any signal of positive polarity being shunted to ground'through the diode. The second differentiating amplifier 22 performs differentiation of the leading and trailing edges of the voltage waveform d, the resulting voltage excursions being indicated by waveform e. The indicated reversal in phase is opposite to the differentiated signal that would be obtained ordinarily by passive RC elements due to the amplification and phase reversal of V4;

The spikelike excursions represented by waveform e undergo successive amplication by amplifier stages 23 and 24, appearing across R64 substantially unchanged except for increase inamplitude. lSince only the positive excursion is of significance, the negative Vhaving no effect, the leading edge of the positiveexcursion of wave- Aform e triggers blocking oscillator 25 into operation. A regenerative action takes place in the windings of transformer T73 further driving the grid of VSA positive until saturation of the transformer results.` A` sharp positive spike voltage represented by waveform j is pro- `i'luceiiinthe output windinglofT73 'anddrives the'monostable multivibrator 26, into operation. V9A ywhich 'is normally cutoff is initiated into plate current rconduction, while V9B normally rconducting is lnow cutoif'unt-il 'such time ,-WhenC82 discharges sut`n`ciently through R83 to allow the grid of V9B 1to a'gainjcause conduction 'in V9B. Grid bias for VSA "is'controlled by R77 which y precisely-controls conduction time or width of the output @pulse represented by Vwaveform g, the trailing edge of 'thisy waveform `being indicated 'as variable relative "to the time base.

The squarewave Voltage 'represented 'by waveform g 's"applied across R91, a proportionate amount depending onfth'e setting'of this vpotentiometer is supplied Yas la gating voltageto the/suppressor grid of grate amplifier 27. This Volt-age is clamped at a l'eve'l established-'by the potential at'the junction of R88 and R89. Hence, pentode "V11 remains cutoff except vduring 'the interval when the lvolt- 'age waveform g becomes suiiiciently positive. The control grid of V11 is continuously suppliedjv'vith positive radar triggers and a number of these appear as inverted negative triggers across R92 when plate Acurrent Ailows i for the duration of the applied 'gating voltage. Thus, it

'will become evident that the beamwidth "of the radar "antenna'will be closely'simulated, the number of target hits Vbeing a function of the duration of the monostable joutput vvoltage of multivibrator 26.

p fThe output of v gate amplier 27 yis represented by Waveform h. This voltage analogous to targetvideo is amplified by amplifier Z8, 'and thepositive ytarget 'video ideveloped across R107 fires blocking oscillator 29 'into operation.v As inthe vprevious instance, positive spikelike signals are developed 4as vindicated by `waveform i. fThese are applied to cathode follower 31, `which vdrives @microwave generator 32. A burst of modulated RF pulses vcoterminous with repetition rate and frequency of the radar'system are'produced as represented by wave- "form'i The RF pulses ,areffed into directional coupler 1'6of "the RF section of the 4radar-system andare subsequently observed Kon 'the PPI Yscreen as detected video `signalscompatible With the regular radar video.

Hence, in -the'mannerset forth the radar target simu I' lator provides forthe generation of 4artificial target 4videro vwhich closelyy resemblesv the 4essential vcharacteristics of rreal target video. Theartiiicial target video conforms to `:radar antenna pattern beamwidth `and may beselectively -i'nljected into the "RF section of the radar system at l "arbitrary range and azimuth. Not only vmay tunable `elements of -t'he radar system by lpeaked Yfor best oper- -at"ion, Vbut also, operator alertness may be monitored at anytime. Thus, theradar -target simulator of the instant invention vprovides fforfthemaintenance of optimum -over- `driving the -delay means of `microwave generator 32.

Furthermore, though the 'target :video produced by the inventivelradar ,targetsimulator (is of constant amplitude, it :may fbe desirable to conform the target video with Jantenna beam .patternand itar'get aspect. Thus, to effect i alternation :ofsignal quality ldue -to :the .reflection proc- -ess, beam pattern,amplitude-modulation could be vadded -if desirable. The ,amplitude vmodulation may be conyenientlyinserted in series with `the cathode lead of gate namplifier 27. Y

AThe .following .tabulation lists illustrative values Y' of electricalcomponents ,used `in the preferred embodiment:

.periodically .recurring AVradar vtriggers and operably C82 H i Y "Af Q A. C63 'Y ,ff f .Q22 C39 .'"f i C79 Y "V'F''-16 C108 auf' 100 C72, C109 ,wirV 25o R43., R52 160 lR58 1K R86 `4K Rm 4.7K R81, R84 p 5K R34, R68, R78, R104 "10K `R91 f Y s Y 16Ky R71, R106 f R11, R38,'R47, R77 1 20K R37 22K 'R64` 24K YR35, R36 25K 'R59 2.7K

R88 39K R93 471K R41 f 450K R42, R49, rR Y l 51K R65, R92, R96, R102, R107 556K R57, R62, R94 100K vR76 `136K vR89 V150K R48 [270K R69, R98, R 390K R45, R46, R55, R56 "470K R44, R53 "11M 'R91 2M T73, T111, 'tertiary Woundjblocking voscillator transformer. v1, vs, V9 V-12;AI7 V2, V7, V10 6A L5 V3, 'V4 6`H'6 V8, V12 '12AU7 V11 n 1a.--. y"6R36 Legend If.=farads nf=microfarad All resistors in ohms It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment'of the invention and Vthat numerous modifications or-alterations .may be made ltherein Without departing from the spirit and the scope ofthe invention as -setforthinthe appended claims.

Whatis clairnedis:

l. In a radar system, a radar target fsimulator ifo generating a target signal closely simulatinglthechara'cteristics of a real target comprising, potentiometer means for producing a voltage proportional in magnitude to instantaneous azimuthal antenna position, voltage y'cornparator means including a diode responsive' to Vsaid-voltage to initiate a signal at an azimuth displaeedinltime position coterrninously with a selected azimuthal antenna position, differentiating amplifier means including '.'feed-I back vmeans responsiveto the voltagecomparatormeans to convert sa'id signal into at least .oneidierentiated 'pulse conforming in time position With the'selectedazimuthll g antenna position, means responsive to said differentiated pulse to produce a sharp spikelike voltage, monostable means responsive to the spikelike voltageto develop .a

gating `potential .of substantially constantrlevel Vfor. a

time duration corresponding `with antenna ,patterngbeann .width, `gating means adapted to be coupled to rasourceof timed "y th gating Potentiel 0f Said mgnosfau netas sgcondi- 7 nto permitsaid gating means to select a discrete number of saidpradar triggers, impedance transformation means includinga blocking oscillator responsive to saidgating means tp convert the selected radar triggers intospikelike voltage excursion ,Ot 19W frrins inrsdaasesnd-micr0- wave generator means including selective amplitude and delay means responsive tothe spikelikefvoltage excursions to generate aV burst of modulated radio frequency jpulses whichlare suppliedto the radio frequency input of theradar system, the modulated radio frequency jpulses thereby being of a characterv closely Vsimulating the Charastaistias. gf real f2-,fest Signals- 2. In a radarnsystern, a'pradar target simulator for jgenerating altarget signal closely simulating the charac- `teristics-of a ral target comprising, potentiometer means for producing ja" voltagApi-oportional in magnitude to instantaneous'Yazimuthal antenna position, voltage com- -paratormeans responsiveqtosaid voltage including a 4diode havingv an element biased atva level corresponding to a selected azimuthal antenna position and operable to initiatea signal at an azimuth displaced in time coterminously with the selected antenna position, differentiating ampliler'means including feedback means responsive tothe voltage comparator means to convert said signal into'at Vleast onedifferentiated pulse conforming in time position with the selected azimuthal antenna position, means responsive to said dilferentiated pulse to produceV a sharp spikelike voltage, monostable means responsive to the' spikelike voltage to develop a gating potential of substantially constant level for a time duration corresponding with antennapattern beamwidth, gating means adapted to be coupled to a source of periodically recurring radar ytriggers and operably conditioned by the gating potential of said monostable means to permit said gating means to select a discrete number of said radar triggers, means responsive to said gating means to convert the selected radar triggers into spikelike voltage excursions of low driving impedance, vand microwave generator means including selective amplitude and delay means responsive to the spikelike voltage excursions to generate a burst of modulated radio frequency pulses which are supplied to the radio frequency input of the radar system, the modulated radio frequency pulses there by being of a character closely simulating the characteristics of real target signals.

3. In a radar system, a radar target simulator for generating a target signal closely simulating the characteristics of a real target comprising, potentiometer means for producing a voltage proportional in magnitude to instantaneous azimuthal antenna position, voltage comparator means responsive to said voltage to initiate a sawtooth signal at an azimuth displaced in time position coterminously with a selected azimuthal antenna position,

differentiating amplifier means including feedback means responsive to the voltage comparator means to convert said sawtoothysignal into at least one differentiated pulse conforming in time position with the selected azimuthal antenna position, means responsive to said differentiated pulse to produce a sharp spikelike voltage, monostable means responsive to the spikelike voltage to develop a gating potential of substantially constant level for a time duration corresponding with antenna pattern beamwidth, gating means adapted to be coupled to a source of periodically recurring radar triggers and operably conditioned by said gating potential to permit said gating means to select a discrete number of said radar triggers, means responsive to said gating means to convert the selected radar triggers into spikelike voltage excursions of low driving impedance, and microwave generator means including selective amplitude and delay means responsive to the spikelike voltage excursions to generate a burst Aof modulated radio frequency pulses which are supplied to the radio frequency input of the radar system, the Ymodulated radio frequency pulses thereby being of a .character closely simulating the characteristics of real Ytarget-signals.

4. In a radar. system, a radar 'target simulator for generating a target signal closely simulating the characteristics of a real target comprising, potentiometer means for producing a voltage proportional in magnitude to instantaneous azimuthal antenna'position, voltage coniparator means responsive to said voltage including a -diode having an element biased at a level corresponding .to a selected azimuthal antenna position to initiate a sawtooth signal at an azimuth displaced in time coter- ,minously with Vthe selected antennaposition, diiferentiat- .ing amplifier means including feedback means responsive to said `voltage comparator means to convert said sawtooth signal into at least one differentiated pulse conforming in time position with the selected antenna position, means including a blocking oscillator responsive to said differentiated pulse to produce a sharp spikelike .delay means responsive to the spikelike voltage excursions to'generate a burst of modulated radio frequency pulses which are supplied to the radio frequency input of the radar system, the modulated radio frequency pulses thereby being of a character closely simulating the characteristics of real target signals.

5. In a radar system, a radar target simulator for generating a target signal closely simulating the characteristics of a real target comprising, means for producing a voltage having a magnitude proportional to instantaneous azimuthal position of a radar antenna, means responsive to said voltage to initiate a sawtooth signal at an azimuth displaced in time coterminously with a selected azimuthal antenna position, a rst differentiating amplifier means including feedback means responsive to said sawtooth signal to produce a bistable voltage having stable upper and lower levels corresponding to the slopes of said sawtooth signal, a second dilferentiating amplifier means including feedback means responsive to said iirst differentiating amplifier means to produce at least one differentiated pulse conforming in time position with the .selected azimuthal antenna position, a first amplifier means responsive to said second differentiating amplifier means to produce in the output thereof an amplified differentiated pulse of phase substantially unchanged relative to the input thereof, a first blocking oscillator responsive to said differentiated pulse to produce a spikelike voltage displaced in time position coincidentally with the selected azimuthal antenna position, a monostable device responsive to said spikelike voltage to develop a `gating potential of substantially constant level for a time duration corresponding with antenna pattern beamwidth, gate amplifier means adapted to be coupled to a source of periodically recurring radar triggers and responsive to the gating potential of said monostable device to select a discrete number of said radar triggers, means including a second blocking oscillator responsive to the gate amplier means to effect a corresponding number of spikelike voltage excursions at low output driving impedance, and microwave generator means includingselective amplitude and delay means responsive to the spikelike voltage excursions to generate a burst of modulated radio frequency pulses which are supplied to the radio frequency input of the radar system, the modulated radio frequenti-spitgfgtterebyj-bang sf;

Y ,ze charger; Ycl'ttly simulatingtheharacteristics of real Irg'et' signals.V A

[6. y In aradar system;airadar.r target simulator forgenerating a target ,signal closely-simulatingthe'characteristicsoffa real'targetjcomprising, meansl for producing av'olta'ge'having: amagnitudeproportional to instante; neous" azimuthal position of; a radar. antenna, V means re-A` sponsive to `saijd vvoltageto initiate a sawtooth signalat an* azimuthV displaced` Ain time coterminously' e with vra selected azimuthal antenna, position, a first differentiating amplifier means including feedback vmeans responsive. to saidsawtooth signal tofpro'ducea bistable voltage having stable upper and lower,levels-corresponding to the' slopes .of saidsawtooth signal, asecond diiferentiatingramplifier means including feedbackmeans responsive to said rst differentiating vamplifier means to produce atleast one Adifferentiated pulse conformingfin time position with the selected azimuthal.antennapositiom amplifier means responsive ,tolV said secondi,differentiatingY amplitiermeans to p'rodu'ce in the output thereof an amplified differentiated pulse of phasesubstantiallyV unchanged relative Yto the input thereof, blocking oscillator means responsive tosaid differentiated .pulse to produce a spikelike voltage displaced .in time position coincidentally withv the selected azimuthal antenna position, a monostable deviceresponsive .to said spikelike voltage to develop a gating potential ofk substantially constant level for al time duration corresponding with lantenna pattern beamwidth,'gate amplifier sponsive to the output excursions of said cathode fol,-y

means adapted tov be coupled to a source of periodically recurring radar triggers and responsive to the gating potential ofrsaid. monostable device to select a discrete ntmibervof` said radar triggers, means responsive to the gate amplifier tol effect a corresponding discrete `number I Y ofv amplified spikelike voltageiexcursions, a cathode follower responsive to the last-named means to supply in the output thereof the spikelike voltageexcursions vat low impedance, and'microwave-generator means .including v' selective amplitude anddela'y means responsive to the .l output excursions of said cathode follower means ,to `generate a burst of modulated radioV frequency pulses-,which are supplied to the radio frequency input of the radar system, the: modulated radioy 'frequency pulses thereby being of a character closelysimulating the characteristics of real target signals.

l 7; In a radar systema radartarget simulator for generating a targetgsignal closely., simulating the characteristics of a real target comprising, means for producing Va voltage having a magnitude proportional to instantaneous azimuthal position of a radar antenna, means'responsive to said voltage to initiate a sawtooth signal at an azimuth l displaced in time coterminously with a selected azimuthal antenna position, a first differentiating amplifier means including feedback means responsive to said sawtooth signal to produce a bistable voltage having stable upper l and lower levels corresponding to the slopes of said sawtooth signal, a second'differentiating amplifier means including feedback means responsive to said first differentiating amplifier means to produce at least one differentiated pulse conforming in time position with the selected azimuthal antenna position, a first amplifier means responsive tosaid second differentiating amplifier means to produce in the output thereof an amplified differentiated pulse of phase substantially unchanged relative to the input thereof, a first blocking oscillator means responsive to said differentiated pulse to produce a spikelike voltage displaced in time position coincidentally with the selected azimuthal antenna position, a monostable device responsive to said spikelike voltage to develop a gating potential of substantially constant level for a time duration corresponding with antenna pattern beamwidth, gate amplifier means adaptedto be coupled to a source of periodically recurring radar triggers and responsive to the gating potential of said monostable device to select ra discrete number of said'radar triggers, a second amplifier means responsive to the gate amplifier means to t t l0 t. produce a corresponding numberof amplifiedrad gers, aseeondgbleeking .oscillator means i-esponsilv4 the amplified Vradar triggersto eecta corresponding number ,of spikelikejvoltage excursions,a cathode, yfol lower means "responsive to the Ylast-named 4blocking oscil,

lator to ,supply inthe output'thereof the spikelike voltage excursions at .low impedance, and microwave generator means including selective amplitudeand delay means relower means to generate a burst of modulated radio fre? quency pulses which. are supplied to the radioV frequency e' input of the radar system, themodulated radio frequency pulses thereby being of acharacter closely simulatingthe characteristics of realwtarget signals. i .s Y

8. InY a radar system, a radar target simulator ffor generating a target signal closely; simulating the char-k acteristics of a real target comprising,l potentiometer means for producing a voltage havinga magnitude '.pro-

poitional to instantaneous azimuthal position of rva radar antenna, means responsive to said voltage to initiate `a sawtooth signal at an azimuth displaced in time ootcrfY minously with a selected lazimuthal antenna position, a

first differentiating amplifier means including feedback means responsive to said sawtooth signal to produce a` bistable voltage having stable upper and lower levels corresponding to theslopes of said sawtooth signal, means operable to provide a unidirectional lowl impedance path to the upper level of said bistable voltage to effect a substantially squarewave pulse, a secondu differentiating amplifier means including feedback meansl for Vdifferentiating said squarewave pulse to produce at least one differentiated pulse conforming in time position with the selected azimuthal antenna position, a lirst Vvoltage amv plifier means responsive to said second diiferentiating amplifier means to produce in the output `thereofan amplified differentiated pulse of phaseV substantially unchanged relative ito-the' input thereof, a1 first blocking oscillator means'responsive to said differentiated pulse to ,produce a spikelike voltage displaced in time position coincidentally with the selected azimuthal antenna position, a monostable device `responsive to said-spikelike voltage to develop a gating potential ofsubstantiajlly constant level for a time duration Vcorresponding -with antenna pattern beamwidth,igate amplifier'means adapted thereof the spikelike voltage excursions at low, impedt ance, and microwave generator means including selective amplitude and delay means responsive to the `output excursions of said cathode follower means to generate a burst of modulated radio frequency pulses which areV supplied to the radio frequency input of the radar system, the modulated radio frequency pulses thereby being of a character closely simulating the characteristics of real target signals.

9. In a radar system, a radar target simulator for generating a target signal closely simulating the characteristics of a real target comprising, potentiometer means for producing a voltage having a magnitude proportional to instantaneous azimuthal position of a radar antenna, means responsive to said voltage including` a diode having an element biased at a level proportionate to a selected azimuthal antenna position to initiate a sawtooth signal at an azimuth displaced in time coterminously with the selected azimuthal antenna position, a first differentiating amplifier means including feedback means responsive to said sawtooth signal to, produce a' bistable voltage having stable upper and lower levels corresponding to the slopes of said sawtooth signal, means operable to provide a unidirectional low impedance path to the upper level of said bistable voltage to effect a substantially squarewave pulse, a second differentiating amplifier means including feedback means for diiierentiating said squarewave pulse to produce at least one differentiated pulse conforming in time position with the selected azimuthal antenna position, a rst voltage amplier means responsive to said second diierentiating means to produce in the output thereof an amplied differentiated pulse of phase substantially unchanged relative to the input thereof, a first blocking oscillator means responsive to said differentiated pulse to produce a spikelike voltage displaced in time position coincidentally with the selected azimuthal antenna position, `a monostable device responsive to said spikelike voltage to develop a gating potential of substantially constantv level for a time duration corresponding with antenna pattern beamwidth, gate amplier means adapted to be coupled to a source of periodically recurring radar triggers and responsive to the gating potential of said -monostable device to select a discrete number of said radar triggers a second voltage amplifier means responsive to the gate amplifier means to produce a corresponding number of amplified radar triggers, a second blocking oscillator means responsive to the amplified radar triggers to eiect a corresponding number of spikelike voltage excursions, a cathode follower meansA responsive to the last-named blocking oscillator to supply in the output thereof the spikelike voltage excursions at low impedance, and microwave generator means including selective amplitude and delay means responsive to the output excursions of said cathode follower means to generate a burst of modulated radio frequency pulses which are supplied to the radio frequency input of the radar system, the modulated radio frequen'cypulses 4being of a character closely simulating the characteristics of real target signals.

l0. In a radar system, a radar target simulator for generating a target signal closely simulating the characteristics of a real target comprising, potentiometer means for producing a voltage having a magnitude proportional to instantaneous azimuthal position of a radar antenna, means responsive to said voltage including a dio'de having an element biased at a level proportionate to a selected tiating means including a feedback voltage amplierresponsive tosaid sawtooth signal to produce a` bistable 'voltage having stable upper andlower levels corresponding to the slopes of said sawtooth signal, diode means operable to provide a unidirectional low impedance path to the upper level of said bistablevoltage to eifect a substantially squarewave pulse, a second differentiating means including a feedback voltage amplifier for differentiating said squarewave pulse to produce at least one differentiated pulse conforming in time position with the selected azimuthal antennaposition, a rst amplifier means responsive to said second differentiating means to produce in the output thereof an amplied differentiated pulse of phase substantially unchanged relative to the input thereof, a first blocking oscillator means responsive to said diiierentiatedpulse to produce a spikelike voltage displaced in time position coincidentally with the selected azimuthal antenna position, a monostable device including a variable bias means responsive to said spikelike voltage to develop a gating potential of substantially constant level for a selectively variable time duration to permit correspondence with yantenna pattern beamwidth characteristics, gate amplifier means adapted to be coupled to a source of periodically recurring radar triggers and responsive to the gating potential of said monostable means to select Ia discrete number of said radar triggers, a second amplifier means responsive to the gate amplier means to produce a corresponding number of amplied radar triggers, a Vsecond blocking oscillator means responsive to the amplified radar triggers to effect a corresponding number of spikelike voltage excursions, a cathode follower means responsive to the last-named lblocking oscillator to supply in the output thereof the spikelike voltage excursions at low impedance, and microwave generator means including selective amplitude and delay means responsive to the output excursions of said cathode follower means to generate a burst of modulated radio frequency pulses which are supplied to the radio frequency input of the radar system, the modulated radio frequency pulses being of a character closely simulating the characteristics of real target signals.

Ginzton Apr. 27. 1948 Okrent Dec. 25, 1956 

